Prince Andrew's office yesterday confirmed that he had sold his home for £15m to buyers from Kazakhstan, but denied that the allegedly inflated price for the property was related to any business deals.

The new owner of Sunninghill Park in Ascot was reported by the Sunday Times to be Kazakh tycoon Kenes Rakishev, who the newspaper alleged had had business dealings with Prince Andrew.

The Sunday Times claimed that the sale of the prince's 12-bedroom former home, which had been on the market for five years, was for £3m more than the upper guide price of £12m. The sale was completed last September. Yesterday a source close to Prince Andrew said the price had been agreed a few months earlier, well before the credit crunch loomed.

The prince, who has an unsalaried role as roving trade ambassador for Britain, has visited the oil and uranium-rich central Asian state on official and private business in recent years, and returned from a private trip at the weekend. A spokesman for Prince Andrew was unable to confirm to the Guardian the name of the buyer, but denied any impropriety. The sale, he said, was "a straight commercial transaction" and added: "There were no side deals and absolutely no arrangement for the Duke of York to benefit otherwise or to commit to any other commercial arrangement. Any suggestion otherwise is completely false." Sunninghill was a wedding present from the Queen to the prince and his then wife, Sarah Ferguson.

The sale was between two trusts - one acting for the prince and including Sir Alan Reid, keeper of the privy purse and the Queen's solicitors Farrar's - and the other said by the Sunday Times to be an offshore company for Rakishev and his father-in-law, a former Kazakh prime minister.

A Labour MP, Ian Davidson, demanded to know if the prince had paid tax on any profit he had made from the sale. "He clearly no longer needs any financial support for his living costs if he is able to make £15m from a house I understand was a present to him," he said.

The prince's spokesman said: "We are confident all tax and legal requirements were complied with."

The government is thought to spend about £500,000 a year on supporting the prince's travel and incidental expenses when he acts as the UK's special representative for trade and investment. The cost of his private office, £249,000 a year, is said by Buckingham Palace to be met from the Queen's private funds.

The prince has been to Kazakhstan in his official role three times since 2003, and is patron of the British-Kazakh Society, founded in 2002 to promote relations between the two countries. The Kazakh president, Nursultan Nazarbayev, is the other patron of an organisation whose sponsors include Shell, the London Stock Exchange and BAE Systems.